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Wierd fuel pressure problem
Posted By: therocks
Wierd fuel pressure problem - 05/27/10 03:14 PM
Had the 440 out last week.Fuel pressure started to drop.Went to probally 3 to 4 psi.I figured maybe the Holley mech pump was going.Put my Carter hipo pump on.Started it and had 6 psi.Took it out last night and pressure was 3 to 4 and goiing to 1 at 50 mph.Today I hooked up my test gauge and had 4 to 5 psi idling.Id think the rod.Only thing I cant figure is why it had 6 to 7 when I first hooked up the Carter.I have great flow from the tank witj 3/8 line.Thought maybe my Auto meter gauge was bad but I doubt my test gauge is also.Just seems at 1 to 2 psi my Dominator would run out of fuel.So do you think the push rod might be bad?Whats the OE length?Rocky
Posted By: ireland383
Re: Wierd fuel pressure problem - 05/27/10 03:18 PM
OE is 3 1/4 inches. How is your fuel line? Do you still have the winter blend in it?
Posted By: therocks
Re: Wierd fuel pressure problem - 05/27/10 03:27 PM
Fuel line is all great.Has just had gas in it.I put 25 bucks worth in last week.Was empty or almost there a month ago.Rocky
Posted By: ireland383
Re: Wierd fuel pressure problem - 05/27/10 03:36 PM
What I found happening on my car was the header was close to the mechanical pump and boiling the gas at it. What's weird is it didn't happen last year. I also found a worn fuel pump pushrod that same season. I wound up going to electric. Check the length on the rod and report back.
Posted By: therocks
Re: Wierd fuel pressure problem - 05/27/10 03:54 PM
Pulled the rod its just shy of 3 1/4 inches.My mics are in my big box and I can get to them.My headers are pretty much away from the pump and lines.Been on for 20 years and never had amy proble.Even cold the pressure is down.Im wondering if the sock might be a problem.Its new as is the sender only like 3 years and 3/8s.I did notice on the cam side the rod looks like it might be mushrooming a bit.Its real shiny the pump side is only shiny on one part.Rocky
Posted By: Challenger 1
Re: Wierd fuel pressure problem - 05/27/10 04:02 PM
Quote:
Pulled the rod its just shy of 3 1/4 inches.My mics are in my big box and I can get to them.My headers are pretty much away from the pump and lines.Been on for 20 years and never had amy proble.Even cold the pressure is down.Im wondering if the sock might be a problem.Its new as is the sender only like 3 years and 3/8s.I did notice on the cam side the rod looks like it might be mushrooming a bit.Its real shiny the pump side is only shiny on one part.Rocky
I'd try a new push rod. My 
Posted By: therocks
Re: Wierd fuel pressure problem - 05/27/10 04:09 PM
I think Ill go over the other garage and get one of my old ones.I know the OE one I pulled was good.This is a MP one I bought probally 11 years ago.It dosent have maybe 5000 miles on it.Rocky
Posted By: ireland383
Re: Wierd fuel pressure problem - 05/27/10 04:09 PM
Both sides of the rod should have a 45 degree bevel around the outer edge. Try to get an exact measurement.
Posted By: 540DUSTER
Re: Wierd fuel pressure problem - 05/27/10 04:10 PM
fill the fuel bowls,disconnect fuel line from carb,start engine with fuel line in a empty gas can and see how much it pumps in 15 seconds.BE CAREFUL AND HAVE FIRE EXT. AT HAND! Also a helper is good to have on the ing. key just in case.
Posted By: therocks
Re: Wierd fuel pressure problem - 05/27/10 04:16 PM
I had it running with my test gauge on it earlier.Still only had like 4 psi.One side looks beved one looks smooth.My fuel filter and bowls were still full even with low pressure.Rocky
Posted By: ireland383
Re: Wierd fuel pressure problem - 05/27/10 04:22 PM
Stick it next to the OE one and check the difference, then put the OE one in.
Posted By: 68HemiB
Re: Wierd fuel pressure problem - 05/27/10 04:22 PM
Quote:
One side looks beved one looks smooth.
My money is on the aftermarket push rod starting to go south. You hang around here enough to have read the sob stories of crappy push rods, and the solution is always to dig out a decent original one. Which it sounds like you are on the road to doing already.
Posted By: VanishPt
Re: Wierd fuel pressure problem - 05/27/10 07:12 PM
Vacumn in the tank ? loosen the cap and see if you hear a WHOOOSH
Posted By: therocks
Re: Wierd fuel pressure problem - 05/27/10 07:14 PM
Well I was going to get an old one.One of my sons locked the door at the other garage and I dont have a key.So now I have to wait for one of them to get my tall ladder and go thru an upstairs window.That or hope one of the dummys have a key.My sons buddy rents the house and I have the garage and never lock it.Figure out why kids do stuff.Worst part is they are in their 30s.Rocky
Posted By: MNobody
Re: Wierd fuel pressure problem - 05/28/10 03:06 AM
Buddy had the same prob, gas tank vent was plugged. Try loosening your gas cap.
Posted By: therocks
Re: Wierd fuel pressure problem - 05/28/10 05:11 PM
I found one of the old ones.Ill put it in later and see what happens.It looks like it might be just a tad longer than the one I pulled.Hopefully it will fix the problem.Rocky
Posted By: ireland383
Re: Wierd fuel pressure problem - 05/28/10 06:00 PM
Good luck, soak the cam end of that rod with some good oil with zinc or additive. I'm sure you already know that.
Posted By: nz383man
Re: Wierd fuel pressure problem - 05/29/10 08:08 AM
Yes you should replace the rod if it is shorter than 3 1/4" but the pump should still hold pressure with a rod up to 1/4" shorter & if it dosn't you have other problems as well.
If all else is good & you are getting a full stroke on a good pump it will run down to about 3/8" shorter than the factory 3 1/4" without loosing pressure. There will be hundreds of bigblock owners out there that needed to change to an electric pump because they were using too much fuel for the mechanical pump when they only really needed a full stroke of their mechanical pump.
Posted By: Manifold
Re: Wierd fuel pressure problem - 05/30/10 04:22 AM
Figured out today why the "genius" who had my car before me put on a crappy auto parts chain store Purolator electric fuel pump vice using the mechanical still bolted to the motor - push rod wore out. After figuring out the new Carter I put on wasn't moving any fuel, I removed it and pulled the pushrod. It measured only 2 7/8" long.
Guess I best track down an OEM so I don't have to go through this again! I really appreciate all the good advice and information folks take the time to post. Thank you!
Posted By: therocks
Re: Wierd fuel pressure problem - 05/30/10 02:18 PM
Found my old rod.It was a tad longer than the one I took out.Tried the Holley and Carter pumps and still only 4 PSI.I think maybe the cam eccentric might be worn.I might pull the Holley off my kis car and try it.One other question.If I have to go electric do you absolutley need a return line?I might get the Summit pump and reg.My Dominator likes a lot of fuel.Rocky
Posted By: ireland383
Re: Wierd fuel pressure problem - 05/30/10 02:40 PM
I'm using the smaller summit electric that does not require the regulator and have a steady 8 PSI. I don't run a return line. I'm only running a Holley 750 though.
Posted By: Twostick
Re: Wierd fuel pressure problem - 05/30/10 02:58 PM
Did you check the vent yet? Leave the gas cap off and check the pressure again. Are you measuring pressure before or after the filter?
Kevin
Posted By: VanishPt
Re: Wierd fuel pressure problem - 05/30/10 04:13 PM
what he said
Posted By: therocks
Re: Wierd fuel pressure problem - 05/30/10 04:20 PM
Had the cap off and checked pressure before and after the filter.Its the same.I was playing with my old Holley pumps and it looks like the arm on the newer one is short like 1/16 inch than the old ones.I know the one I bought in 71 is shot for sure.The new arm dosent look worn.I wonder if it could be slightly bent?Ill have to pull the carter and see if the arm is as long.Rocky
Posted By: VanishPt
Re: Wierd fuel pressure problem - 05/30/10 04:27 PM
you had the cap off in the same situation as you experienced the low pressure?
Or did you take the cap off a while after the situation?
Posted By: therocks
Re: Wierd fuel pressure problem - 05/30/10 04:29 PM
Checked it with it on and off.Pressure was the same.Rocky
Posted By: VanishPt
Re: Wierd fuel pressure problem - 05/30/10 04:32 PM
did you have the cap off at 50 mph?
Posted By: therocks
Re: Wierd fuel pressure problem - 05/30/10 04:36 PM
No the cap was on doing 50.But If it was bad it would make a difference even idling.I believe the 65 used a non vented cap.Its been on since 65.Rocky
Posted By: Twostick
Re: Wierd fuel pressure problem - 05/30/10 11:12 PM
Could be the sock in the tank. Could also be a collapsed hose. I've even seen rags in a fuel tank blocking the pick up. You usually find something like that AFTER you've replaced the entire fuel system tho
. You could put a tee in the suction hose at the pump and hook up a vacuum gauge. That would tell you if you have a restricted suction line.
Posted By: BobN
Re: Wierd fuel pressure problem - 05/31/10 02:50 AM
I went through this last summer on my 440.
low fuel pressure, stalling, then starting right back up?
running like crap.
opening gas cap seemed to help.
replaced sending unit and fuel pump .
Turned out my fuel pump push rod was 1/2" short on one end/
replaced that rod and all seems find now.